A plasma arc is developed by passing the arc through an arc constricting passageway formed in a nozzle located between the electrode and work. The plasma arc process employs extremely high open circuit voltages and relatively high operating voltages and is rated to operate at high current levels. The rated current capacity depends on the construction of the torch and the plasma arc application. However, even the low current capacity plasma arc torches are rated to operate at high operating current levels, e.g., up to between 30 to 50 amperes. Accidental mishandling of a plasma arc torch while inspecting or replacing the electrode can cause an electrical shock which may be fatal to an operator. To avoid the possibility of an accidental electrical shock, prior art plasma torches have been constructed with electrical contacts incorporated in the torch to interlock the heat shield with an electrical control circuit. This type of safety control is relatively expensive and has in the past proven to be unreliable.